1. Field of the Invention
The present invention relates to a magnetic disk device for storing and reproducing data, and more particularly a data error correction device used when a data error occurs, and the correction method thereof.
2. Description of the Prior Art
Today, magnetic disk devices are used as hard disks or fixed disks for personal computers, etc. The magnetic disk devices have concentric circular tracks for storing data, and one track is composed of a plurality of sectors. A magnetic head shifts in a direction perpendicular to the concentric circular tracks from the outermost track to the innermost track, and writes data in and reads data from the magnetic disk.
Today, miniaturized, large-capacity and high-density magnetic disk devices are required. For this reason, the improvement in both the number of recorded bits per inch (track recording density (BPI) (bits per inch) and the number of recorded tracks per inch (track density (TPI) (tracks per inch)) is indispensable. However, high track recording density causes interference between individual data bits, while high track density causes interference between tracks, both of which degrade the quality of read signals and lead to an increase in data errors. Under these circumstances, if a read error occurs, conventionally parameters are changed according to a rewrite step stored in a storage unit, and the data are repeatedly read until normal data are obtained. For example, by making the cut-off frequency of a filter variable or changing the dimension of a sense current from a pre-amplifier to the magnetic head as such changed parameters, retrying is repeated.
For example, when the dimension of a sense current is variable as a parameter, sense currents changed at intervals of 0.1 mA, that is, 9.1 mA, 9.2 mA, 9.3 mA, . . . , etc. are made to flow in the coil of the magnetic head, and this variable process is repeated until normal data are obtained.
According to the retry method, by repeating a great number of data readings, normal data can be obtained. However, it often takes a lot of time to obtain normal data. For example, when normal data are obtained in a series of steps, the execution of the previous steps takes a lot of time. That is, when the parameter set in the last step is the optimum value of the device, the retry must be repeated until the last step is reached, every time. Such a data reading takes a long time.
An object of the present invention is to provide both a data error correction device and a method thereof for reducing the time needed to obtain normal data by using a retry method and by reducing the frequency of retries.
That is, the object of the present invention is accomplished by providing a disk device comprising a storage unit for storing a plurality of data read conditions set in a plurality of parameters, a data read unit for reading data from a disk according to a first data read condition stored in the storage unit, a data re-read unit for, when an error occurs in data read by the data read unit, changing the first data read condition to a second data read condition and reading data from the disk again, and a replacement unit for, when the error is recovered from and normal data are obtained by reading the data again, replacing the orders of the first and second data read conditions stored in the storage unit.
Each of the first and second read conditions has a plurality of parameters, and the parameters are a variety of read conditions used when data are read from the magnetic disk, and, for example, are individual characteristics of the magnetic disk device. Therefore, by changing the set value of these parameters, data read conditions are changed, and even if normal data cannot be obtained by a first read condition, normal data can be often read by changing the first read condition to a second read condition.
This preferred embodiment has a configuration such that the values of parameters are made variable and when normal data are obtained by changing the data read condition from the first condition to the second condition, the first data read condition is replaced by the second data read condition by the replacement unit.
According to such a configuration, when data are subsequently read from a disk, a time needed to obtain normal data is reduced, and rapid data reading becomes possible.
For example, the data read conditions are stored in the storage unit in units of the same parameter groups, and the replacement unit replaces the data read conditions in units of the groups.
According to such a configuration, when the change of only a certain parameter is effective in recovering from an error, data read conditions can be efficiently replaced, and thereby the retry process of this preferred embodiment can be rapidly executed.
In the group replacement, for example, the counter unit counts error recovery frequency. When the value reaches a predetermined threshold, the replacement of data read conditions is performed for each parameter group.